This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A015580 #48 Dec 18 2023 12:19:24
%S A015580 0,1,9,85,801,7549,71145,670501,6319089,59553805,561260601,5289560629,
%T A015580 49851088065,469818035101,4427766668169,41729172153925,
%U A015580 393273616058001,3706379233137709,34930507562471385,329200084994793301,3102522795203025249,29239505496806400445
%N A015580 Expansion of x/(1 - 9*x - 4*x^2).
%C A015580 Pisano period lengths: 1, 1, 2, 1, 3, 2, 48, 2, 6, 3, 10, 2, 42, 48, 6, 4, 24, 6,360, 3, ... - _R. J. Mathar_, Aug 10 2012
%H A015580 Vincenzo Librandi, <a href="/A015580/b015580.txt">Table of n, a(n) for n = 0..1000</a>
%H A015580 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (9,4)
%F A015580 a(n) = 9*a(n-1) + 4*a(n-2).
%t A015580 LinearRecurrence[{9, 4}, {0, 1}, 30] (* _Vincenzo Librandi_, Nov 14 2012 *)
%o A015580 (Sage) [lucas_number1(n,9,-4) for n in range(0, 19)] # _Zerinvary Lajos_, Apr 26 2009
%o A015580 (Magma) [n le 2 select n-1 else 9*Self(n-1) + 4*Self(n-2): n in [1..30]]; // _Vincenzo Librandi_, Nov 14 2012
%o A015580 (PARI) x='x+O('x^30); concat([0], Vec(x/(1-9*x-4*x^2))) \\ _G. C. Greubel_, Jan 06 2018
%Y A015580 Cf. A015579, A099371.
%K A015580 nonn,easy
%O A015580 0,3
%A A015580 _Olivier Gérard_
%E A015580 Extended by _T. D. Noe_, May 23 2011